The present invention concerns a pressure infusion apparatus of the type that includes a chamber for receiving at least one infusion bag and in which chamber there is a pressure apparatus operating against the infusion bag for dispensing the infusion liquid through an infusion tube whereby the pressure apparatus includes a pneumatic pressure storage chamber and a pressure applicator.
In connection with acute illness and accidents as well as for therapeutic purposes one often uses intravenous (direct into a blood vessel) injection of liquids in modern medicine. It is an essential step in the prevention of post operative shock. In modern clinical practice glass bottles have long since been abandoned in favor of plastic bags. The latter are lighter, easier to store, better for the patient and superior from the point of view of handling. Nowadays the liquid is almost always stored in plastic bags.
The most usual method of applying the liquid intravenously is to hang up the bag on a support about a meter over the patient and to bring the liquid from the bag to the needle in the vein, usually placed in the arm, via a plastic tube. The flow is regulated by a flow reduction apparatus in the tube and the amount of liquid is controlled by observation of the drop rate in a drop chamber higher up in the tube.
Experienced staff usually know about which drop rate corresponds to a given amount of liquid per unit time. The precision of their judgement is naturally quite variable but great precision is usually not needed. The system usually requires repeated checks during the period of the infusion. When the supply of liquid is to be given to upright patients they have to carry the drop support with them. The same is true for long term nutrition via a tube to the digestive tract.
The technique of compressing bags filled with liquid to dispense liquid is well known in medical applications. There are several different constructions with spring loaded pistons that apply pressure to the bag for that purpose. There are constructions with inflatable rubber balloons which compress the bag for the same purpose. The latter construction requires repeated addition of air pressure, which can be achieved in different ways.
In all cases the mechanical constructions are designed for especially adapted bags which must therefore be marketed together with their contents. This in combination with unsatisfactory flow regulation, mainly based on pressure gradients, and the lack of harmony in the design, at least from the patient""s point of view, means that these new creations have not found wide use in health care.
When a more exactly regulated liquid dosage is required, for instance for giving diluted, potent medicine, cell poisons and the like, these systems are not good enough. Then electronic apparatus is used in which a tube pump function or specially attached pumps on the output tube allow a regulated, programmable very exact dosage. These apparatus are expensive, complicated, require electric power and often require expensive accessories for their function. They are also placed on supports, either freely, on rollers or fixed to the patient""s bed. They are far too expensive to be used in daily routine applications and are not appropriate for treatment of large numbers of patients, for example in the case of catastrophes.
The Swedish publication text nr 467 951 shows an infusion apparatus consisting of an infusion bag and on it a normally permanently fixed infusion tube including an opening tool and a flow indicator, a clip and a stop valve which prevents return flow to the bag. In use the infusion apparatus is placed under the patient to provide pressure.
The Swedish publication text nr 448 822 shows a portable apparatus including a spring for providing liquid at constant pressure for medical or other similar applications. The spring exerts a constant force moment whereby sticking due to possible twisting of the sliding piece on which the spring exerts its force is eliminated.
Also WO 89/11303 shows an apparatus including a spring which exerts an axial force on a vessel containing a liquid in order to squeeze out the liquid.
The German Publication text 2053995 shows a system including a lower and an upper pressure plate which can be provided with a rubber band around the plates to press them together whereby pressure is applied to an infusion bag placed between the plates so that the liquid is squeezed out of the bag.
The purpose of the invention and the solution of the problem
The purpose of the present invention is to achieve an infusion apparatus
which does not depend on an external source of energy,
for which no one need hold the liquid containing bag in acute situations,
for which there is no drop support,
in which the amount of liquid to be given the patient per unit time is easily adjusted,
in which the liquid flow is constant during the infusion making checks and adjustments unnecessary,
in which air is absent from the system, thus eliminating air bubbles,
which is simple and robust and requires few instructions making it especially appropriate in connection with large catastrophes when many people must be treated at the same time,
the price of which is kept low through use of disposable material.
The apparatus can also be used for continuous application of nutrition to the digestive tract through a thin tube.
These purposes have been achieved by placing a pressure reduction valve between the pressure storage chamber and the pressure source thus significantly reducing the pressure in the pressure source relative to the maximum loading pressure in the pressure storage chamber, by equipping the pressure source with an essentially unstretchable, air tight, bendable membrane dividing the chamber into an infusion chamber and a pressure chamber acting directly on the bag, and by making it possible to attach a flow regulating valve giving a calibratable flow per unit time to the infusion bag""s infusion tube or its extension.